The invention relates to a microtome having specimen retraction means.
Retraction of a specimen holder having a specimen clamping mechanism in which a specimen is clamped, relative to a fixed cutting knife after a cut has been made is generally known in microtomy. As a result of this retraction, the cutting knife is protected from damage, so that the useful life of the cutting knife is increased. Also, as a result of this retraction the cut surface of the specimen is protected against scratches and damage during the return movement, so that accurate working is possible.
Retraction of the specimen is necessary particularly in the thin-section cutting of hard specimens or in the thin-section cutting of specimens embedded in plastic, in order to achieve a perfect quality of cut and a long useful life of the cutting knife.
It is also known to provide a cutting thickness adjuster which can adjust the position of the specimen holder, usually towards the cutting knife, by a cutting thickness adjustment distance.
In known microtomes, the size of the retraction of the specimen holder is of an order of magnitude which can be less than the maximum possible cutting-thickness adjustment distance, so that it is not possible to prevent incorrect operation when the distance retraction of the specimen is less than the cutting-thickness adjustment distance. This fact presents problems, particularly when the adjustment of the cutting-thickness takes place not when the specimen holder is in position before a cut, but before this, when it is in its position immediately after a cut and before the return of the specimen holder to the cutting position. Moreover, in known microtomes, the specimen retraction mechanism, is an expensive combination of gear wheel and/or spring mechanisms, which can adversely affect the ease of movement of a microtome of this type. Furthermore, in known microtomes, the drive wheel which is provided for generating vertical movement of the specimen holder in order to execute a cut, can rotate in one direction only.